Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, composite, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
US Patent Application 2007-0096130 describes “a process for forming an LED structure using a laser lift-off process to remove the growth substrate (e.g., sapphire) after the LED die is bonded to a submount.” To eliminate the need to use an underfill between the submount and the LED die to support the die, the underside of the LED die has formed on it anode and cathode electrodes that are substantially in the same plane, where the electrodes cover at least 85% of the back surface of the LED structure. The submount has a corresponding layout of anode and cathode electrodes substantially in the same plane.
“The LED die electrodes and submount electrodes are interconnected together such that virtually the entire surface of the LED die is supported by the electrodes and submount. No underfill is used. Different methods for LED to submount interconnection can be used, such as ultrasonic or thermosonic metal-to-metal interdiffusion (Gold-Gold, Copper-Copper, other ductile metals, or a combination of the above), or soldering with different alloy compositions such as Gold-Tin, Gold-Germanium, Tin-Silver, Tin-Lead, or other similar alloy systems.
“The growth substrate, forming the top of the LED structure, is then removed from the LED layers using a laser lift-off process, which ablates the material at the interface of the growth substrate and the LED layers. The extremely high pressures created during the laser lift-off process do not damage the LED layers due to the large area support of the LED layers by the electrodes and submount. Other substrate removal processes can also be used.